The present invention relates to digital video, and more particularly to a scheme for enabling still picture sequences (sometimes referred to as “still frame” sequences) to be communicated at a very low bit rate (e.g., under 200 Kbps) in the same transport stream that is carrying full motion video, multimedia and/or audio services such as conventional television programming. The techniques of the invention are particularly suitable, e.g., in providing still pictures for weather channels, album covers (e.g., text and graphics) that may accompany music channels, real estate sales channels, home shopping channels, and the like. For example, the invention will enable the album cover of a music video to be displayed while the video is playing, with the album cover video information being provided at a reduced bit rate (and consequent savings in bandwidth) with respect to the full motion music video (i.e., “normal video”).
One prior technique for providing still picture images in a digital television environment involves precompressing the still pictures, storing the precompressed frames, and then providing the stored precompressed frames for decompression and display when requested. This technique is not advantageous since it does not provide real-time processing of the frames and, as a result, requires additional hardware (such as a server) to store the precompressed files and deliver them when required.
Another prior art technique is that used in the Digicipher® II digital television system developed by General Instrument Corporation of Horsham, Pa., U.S.A. In this system, video frames are normally compressed as Predictive (P) frames, and an Intra (I) frame is only processed when specifically requested by a syntax processor. In order to capture a still picture, the syntax processor instructs the video compressor to go into a still frame mode by setting a still frame mode flag. This causes the compressor frame buffer pointers to freeze, which in turn causes the same frame to be repeated. When a new frame is to be captured, the syntax processor first disables the still frame mode flag to the compressor, and the compressor returns to a normal video mode operation. To capture a new still picture, the still frame flag is set again. This sequence of operation adds complexity due to the requirement to set and re-set the still frame mode flag and to switch the compressor between P-frame and I-frame processing.
Accordingly, it would be desirable to provide simplified and less costly apparatus and methods for encoding and transmitting still picture images, and for transmitting such images at reduced frame and transmission rates, using the MPEG-2 or similar standard. It would be further advantageous to provide such apparatus and methods that can be implemented using a standard video compressor that operates in the same manner and using the same algorithms for both still pictures and normal video. It would be still further advantageous to provide such apparatus and methods that will operate with a conventional decoder, without the need for a special still frame decoder mode. Such a scheme would advantageously utilize the MPEG-2 “still picture mode” at the decoder.
An advantageous system as described above would provide a bandwidth efficient and cost effective solution to the communication of still picture images for digital television and the like. The present invention provides methods and apparatus having the aforementioned and other advantages.